In an operation system in which an operator and a machine conduct working in cooperation with each other, for example, in an operation system using a press in which a slide reciprocated through a connecting rod by a crank rotated synchronously with a motor, is manually operated by an operator, the safety measure for the operator is very important.
In the aforementioned operation system, it is important to ensure safety by monitoring overrun of the slide by determining operating conditions in the slide operation process on the press side and also by an optical safety device disposed before a bolster.
The safety measures will be logically explained as follows.
A job site S (a region on a bolster in the case of a press) is studied here in which an operator and a movable portion of a machine (a slide in the case of a press) conduct working in cooperation with each other. A logic variable H(t) represents that the operator is present in job site S at time t. A logic variable M(t) represents that the movable portion of the machine exists in job site S at time t. H(t)=1 represents that the operator is working in job site S at time t, and H(t)=0 represents that the operator is not working in job site S. M(t)=1 represents that the movable portion of the machine is operated in job site S at time t, and M(t)=0 represents that the machine is not operated.
In this case, consideration is given to a form in which the operator and the movable portion of the machine are existing in job site S, and Hs(t) represents that the operator is in job site S while he is working in a correct operation, and Ms(t) represents that the movable portion of the machine is in job site S while it is being operated in a correct operation. Further, Hf(t) represents that the operator is mistakenly in job site S, and Mf(t) represents that the movable portion of the machine is in job site S due to a breakdown or an influence of noise. (Hs(t).multidot.Hf(t)=0, and Ms (t).multidot.Mf(t)=0)
Therefore, Hs(t)=1 or Ms(t)=1 represents that the operator or the movable portion of the machine is rightly working in job site S at time t. Hf(t)=1 or Mf(t)=1 represents that the operator or the movable portion of the machine is incorrectly working in job site S at time t. Hs(t)=0 or Ms(t)=0 represents that the operator or the movable portion of the machine is not working in job site S at time t in the form of a correct operation. Hf(t)=0 or Mf(t)=0 represents that the operator or the movable portion of the machine is not working in job site S at time t in the form of a incorrect operation.
When consideration is given to mistaken operations as described above, the operation of the operator or the movable portion of the machine is either a normal operation or a mistaken operation. Therefore, the working state H(t) of the operator in job site S at time t and the working state M(t) of the movable portion of the machine in job site S at time t can be expressed by the following expressions. EQU H(t)=Hs(t) V Hf(t) (1) EQU M(t)=Ms(t) V Mf(t) (2)
where V represents a logical sum.
In the aforementioned operation system, the occurrence of an accident is defined as follows: the operator and the movable portion of the machine operate together at the same time in the same space, that is, a collision occurs. Accordingly, in order to safely carry out the operation in this operation system, the following expression must be satisfied at time t. EQU H(t).multidot.M(t)=0 (3)
where.multidot.represents a logical product.
That is, the following expressions must be satisfied. ##EQU1##
The aforementioned expression (4) expresses the principle of a safety operation, that is, the expression (4) means that: in the case where the operator and the movable portion of the machine share job site S with each other, not only when both the operator and the movable portion of the machine operate rightly but also when one of the operator and the movable portion, or both of them operate incorrectly, the occurrence of collision must be prevented.
In the case where the operation system is set so that the aforementioned principle of safety operations can be satisfied, the expression Hs(t).multidot.Ms(t)=0 must be satisfied when the operator and the movable portion of the machine are in a normal operating condition. Therefore, in order to ensure the safety of operations even when a mistaken operation is conducted, the following expression must be satisfied. EQU {Hs(t).multidot.Mf(t)} V {Hf(t).multidot.Ms(t)} V {Hf(t).multidot.Mf(t)}=0(5)
The above expression is a condition to be satisfied even when an operation is mistakenly carried out.
Expression (5) is satisfied when the operation is carried out in the following manner: even when a mistaken operation that neither the operator nor the movable portion of the machine starts working, is caused, that is, even when a mistaken operation on the side of Hf(t)=0 or Mf(t)=0 is caused, both mistaken operations of Hf(t)=1 and Mf(t)=1 are not caused. In other words, expression (5) is satisfied when there are no mistaken operations on the sides of the operator and the movable portion of the machine, that is, expression (5) is satisfied when neither expression Hf(t)=1 nor expression Mf(t)=1 is satisfied. This means that: when both the operator and the movable portion of the machine are provided with fail-safe properties (properties in which operations are not started mistakenly), that is, when both expression Hf(t)=0 and expression Mf(t)=0 are satisfied, expression (5) can be satisfied. The aforementioned operation system can be realized by the structure in which an output on the side of the movable portion of the machine is generated when it has been detected that the operator is not present in job site S, and also in which the operation on the side of the operator is started when it has been confirmed that the movable portion of the machine is not in job site S. That is, the aforementioned operation system can be realized by the structure of an interlock system of the operator and the machine. The logical expression to ensure safety is expressed as follows: EQU H(t)=h(t).multidot. M(t) EQU M(t)=m(t).multidot. H(t) (6)
(Mark expresses a negation in the above expressions.) where the operation command of the movable portion of the machine is m(t), the output to conduct working is M(t), the will of working on the operator's side is h(t), and the behavior to conduct working is H(t), and each of them is expressed by binary logic variables (1 and 0).
Expression (5) is given by the sum of three logical products Hs(t).multidot.Mf(t), Hf(t).multidot.Ms(t) and Hf(t).multidot.Mf(t). Therefore, even when a mistaken operation such as Hf(t)=1 or Mf(t)=1 occurs, no problem is caused when the sum of the logical products is a logical value 0. For example, when a mistaken operation Hf(t)=1 of the operator is caused, no problem is caused when the movable portion of the machine is not operated, that is, no problem is caused as long as neither Ms(t)=1 nor Mf(t)=1. In the case where a mistaken operation Mf(t)=1 of the movable portion of the machine is caused, no problem is caused unless the operator starts working, that is, no problem is caused as long as neither Hs(t)=1 nor Hf(t)=1. The structure to ensure safety according to expression (6) must be provided with the following function on the side of the movable portion of the machine: the function to detect that the operator is not present in job site: and the function to control the movable portion side so that the movable portion side can not mistakenly generate an output. Also, the structure to ensure safety must be provided with the following function on the side of the operator: the function to check that the movable portion of the machine is not present in the job site; and the function to control the operator so that the operator never goes to the job site. However, it is essentially impossible for the operator to conduct working without making any mistakes in an actual operation. Also, the operation command generated on the side of the movable portion of the machine is not necessarily generated without mistakes. Therefore, in order to realize the operation system in which the operator and the machine conduct working in cooperation with each other, there is no way except for adopting the following system: on the assumption that the worker does not intentionally collide against the movable portion of the machine, the movable portion of the machine conducts working at least only when the operator is not present in the job site; and a countermeasure is taken on the side of the movable portion of the machine so that any mistakes are not made when working is carried out.
FIG. 1 is a schematic illustration showing a model of an operation system in which the operation is carried out without relying on the confirmation and judgement of safety made by an operator (for example, the confirmation and judgement of safety based on visibility), wherein it is acknowledged that the operator can not help making a mistake when he confirms and judges the safety of operation.
In FIG. 1, Character S denotes a job site in which the movable portion of the machine and the operator conduct working in cooperation with each other, I.sub.M1 denotes a sensor detecting that the worker is not present in job site S, I.sub.M2 denotes a sensor detecting that there is no mistake on the machine side (in the case of a press, on the side of a controller that generates operation command m(t)), and G.sub.M1 and G.sub.M2 are logical product components that show the judging function. The operation command m(t) on the machine side is made as follows: after sensor I.sub.M1 has confirmed that the operator is not present in job site S, output command Ma(t)=(m(t).multidot. H(t)) is generated in accordance with the result of the judgment. This output command Ma(t) is made in the following manner: output M(t) to carry out the operation is generated after sensor I.sub.M2 has confirmed that the machine side is normal so that the output can not be mistakenly sent due to a failure on the machine side while the operator is in a working condition. When sensor I.sub. M2 and logical product component G.sub.M2 are realized, being provided with fail-safe output properties in which output M(t) to carry out the operation is not mistakenly generated, output M(t) on the machine side can be expressed by the following expression. EQU M(t)=m(t).multidot. H(t).multidot.Ma*(t) (7)
The meaning of expression (7) is as follows: only when the operator is not present in job site S ( H(t)=1) and the machine side is normal (Ma*(t)=1), execution output M(t) obeys operation command m(t). Ma*(t) is a logic variable representing the operating condition on the machine side. It is a binary value that expresses a logical value 1 in the case of a normal operating condition, and a logical value 0 in the case of an abnormal operating condition.
That is, in order to satisfy expression (7) for ensuring the safety of an operation system in a press in which the operator and the machine conduct working in cooperation with each other, it is necessary to provide the function to detect that the operator is not present on the bolster, that is, the confirming function of H(t)=1, and also it is necessary to provide the function to detect that the machine is normal, that is, the confirming the function of Ma*(t)=1. In the case of a press, the former function is provided by an optical type safety device structured in such a manner that: a light beam is formed before the bolster; the light beam is intercepted by the body of the operator who is present on the bolster when the slide is lowered; and the lowering motion of the slide is stopped when the light beam is intercepted. The latter function is a fail-safe overrun monitoring function in the sliding operation control that is operated in such a manner that: only when the machine side including sensor I.sub.M1 and logical product component G.sub.M1 is normal, the output to lower the slide is generated; and at the same time, the braking function is confirmed so that the slide can be positively stopped at the time when the slide ought to be stopped.
Monitoring of overrun of the slide in the slide operation control in a press is conducted in such a manner that: it is confirmed whether or not the slide is raised and stopped in a predetermined range. However, in general, it is difficult to confirm in a short period of time that a body has been completely stopped in a mechanical system. Therefore, whether or not the slide has overrun in a press is judged in such a manner that: after a stop command has been given to the slide in the process of rising, the slide is restarted; and at that time, the position of the slide is confirmed. For example, in the case of a mechanical press in which the number of strokes is not more than 150 in a minute, the following structure is required: when the slide is stopped in a range of not more than 15.degree. of the crank angle after the crank angle has passed through the top dead point of the slide, it is judged that the slide can be restarted; and when the slide has passed through the crank angle of 15.degree., it is judged that the slide has overrun, so that the slide can not be restarted.
It is important that the monitoring method of overrun is provided with the following functions.
(1) The drive source of the slide ought to be shut off in a predetermined position in the elevating process of the slide.
(2) The operation button of the slide is turned off when the slide is restarted.
The function of item (1) has the following meaning. Even when a shut-off operation is conducted too early, the slide is stopped in a predetermined range in the case where the brake has been deteriorated and the braking distance has been extended longer than that in a normal condition. In the aforementioned case, there is a possibility that the operation is mistakenly judged to be normal. The aforementioned function of item (1) prevents the misjudgment described above. Concerning the shut-off function, in the case where the shut-off timing is delayed, the overrun of the slide can be positively judged when the brake is deteriorated. Therefore, the mistake on the delay side can be allowed.
The function of item (2) has the following meaning. In the case where the operation button has a problem on the side of ON, the slide is restarted when the slide passes through the top dead point even if the braking performance is deteriorated and the slide is in an overrunning condition. In order to take measures to meet the aforementioned situation, the item (2) means that the operating conditions of the press ought to include a checking operation to check that the start button is in an OFF condition in the elevating process of the slide.
Accordingly, in order to conduct working safely using a press, it is necessary to provide a function in which the operation of the slide is carried out at least only when the operator is not present on the bolster. That is, in addition to the optical safety device, it is necessary to provide the function of monitoring overrun (confirmation of the brake performance) in order to prevent the slide from being mistakenly lowered while the operator is present, and it is also necessary to provide the function of confirming that the operation button is turned off. The aforementioned overrun monitoring function (the brake performance checking function) and the operation button OFF checking function must be realized in such a manner that they are made in a fail-safe structure, that is, in a structure in which the slide is not lowered in the case of a failure.
In order to ensure the safety of the operator in the press working in which the operator and the machine cooperate with each other, it is very important to have the overrun monitoring circuit and the operation button OFF checking circuit composed of a failsafe structure in the slide operation control circuit.
Conventionally, a contact circuit provided with an electromagnetic relay is used for the slide operation control device of a press including the aforementioned overrun monitoring circuit and the operation OFF checking circuit. In this case, it is necessary to give consideration to a problem of the contact of the relay in which the point can not be opened, that is, a problem in which the contact is melted and deposited. In order to take measures to solve the aforementioned problem, for example, a sequential interlock structure (a back-check circuit) is conventionally adopted.
It is structured in the following manner: since the position of each relay is in an ON or OFF condition in accordance with the operating position of the slide, other relays adopt the conditions to conduct the successive operation so that each relay can be sequentially operated. Specifically, the sequential interlock structure is composed in such a manner that: the state of a normally closed contact is used for a proof of OFF of the contact; and the proof is taken for the exciting condition of another relay so that each relay is sequentially operated. According to the aforementioned sequential structure, when a specific contact is in a problem in which the contact is in an ON condition, the normally closed contact can not be closed, so that the exciting condition of another relay can not be satisfied. Therefore, the operation is stopped.
However, in the contact circuit in which the aforementioned relay is used, it is necessary to employ the interlock structure for all relays. Therefore, the number of relays, that is, the number of contacts is increased, so that the circuit structure becomes complicated, which is disadvantageous.
Even when the sequential interlock structure is adopted, the operation can not be necessarily stopped in the case where the melting and depositing problem has concurrently occurred in a large number of relays. Consequently, the sequential interlock structure is not sufficient from the viewpoint of reliability.
In view of the aforementioned circumstances, it is a primary object of the present invention to provide a highly reliable slide operation control device of simple structure used for a press, wherein the overrun monitoring circuit and the operation button OFF checking circuit of the slide operation control device are composed of an electronic circuit based on fail-safe signal processing.